The broad objective of this project is to elucidate the processes by which the cardiovascular system responds to the stress of physical exercise. Utilization of techniques developed by the investigator permit accurate, continuous measurement of left ventricular internal diameter and pressure, as well as pressures and flows in major vessels using chronically implanted electronic devices in dogs exercising on a treadmill. Specific investigations involving exercise stress will be made of factors determining myocardial oxygen consumption during exercise, effects of plasma volume expansion and contraction, effects of manipulation of red blood cell mass, autonomic control mechanisms during recovery from exercise, effects of selected disease models and effects of conditioning and deconditioning.